add code

dca0/pcm.go

@@ -0,0 +1,73 @@
+// Helper functions for extracting pcm audio from web and local sources.
+package dca0
+
+import (
+	"errors"
+	"io"
+	"os/exec"
+	"strconv"
+)
+
+type PcmOptions struct {
+	FfmpegPath string
+	Channels   int
+	SampleRate int
+	// Seek means where to start in seconds.
+	Seek float32
+	// Duration means where to stop (in seconds after the time specified by Seek).
+	// If Duration is set to 0, the stream will ignore it and encode all the way
+	// to the end of the input.
+	Duration float32
+}
+
+func getDefaultPcmOptions(ffmpegPath string) PcmOptions {
+	return PcmOptions{
+		FfmpegPath: ffmpegPath,
+		Channels:   2,
+		// 48000 is the only one used by discord currently.
+		SampleRate: 48000,
+		Seek:       0,
+		Duration:   0,
+	}
+}
+
+// Input can be either a local file or an http(s) address. It can be of any
+// audio format supported by ffmpeg.
+// Wait must be called on the returned command to free its resources after
+// everything has been read.
+func getPcm(input string, opts PcmOptions) (io.ReadCloser, *exec.Cmd, error) {
+	if input == "" {
+		return nil, nil, errors.New("dca0.getPcm() called with empty input")
+	}
+	var cmdOpts []string
+	cmdOpts = append(cmdOpts, []string{
+		"-vn", // No video.
+		"-sn", // No subtitle.
+		"-dn", // No data encoding.
+	}...)
+	if opts.Seek != 0.0 {
+		cmdOpts = append(cmdOpts,
+			"-accurate_seek",
+			"-ss", strconv.FormatFloat(float64(opts.Seek), 'f', 5, 32))
+	}
+	if opts.Duration != 0.0 {
+		cmdOpts = append(cmdOpts,
+			"-t", strconv.FormatFloat(float64(opts.Duration), 'f', 5, 32))
+	}
+	cmdOpts = append(cmdOpts, []string{
+		"-i", input,
+		"-f", "s16le", // Signed int16 samples.
+		"-ar", strconv.Itoa(opts.SampleRate),
+		"-ac", strconv.Itoa(opts.Channels), // Number of audio channels.
+		"pipe:1", // Output to stdout.
+	}...)
+	cmd := exec.Command(opts.FfmpegPath, cmdOpts...)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return nil, nil, err
+	}
+	if err := cmd.Start(); err != nil {
+		return nil, nil, err
+	}
+	return stdout, cmd, nil
+}